Recovery of gasoline



3m 1940- R. c. LASSIAT 2,186,029

RECOVERY OF GASQLINE Filed Feb. 27, 1937 w auoz e w Crac king INVENTQR Rcamnrqd llLclssicli' T I ATTORNEY Patented Jan. 9, 1940 PATENT OFFICE naoovnnr or oasonmn Raymond C. Lassiat, Swarthmore, Pa., assignor to Houdry Process Corporation, Wilmington, Del., a corporation of Delaware Application February 27, 1937, Serial No. 128,112

6 Claims. (01. 196-10) This invention relates to the production, separation and recovery of light or low boiling hydrocarbons especially liquid hydrocarbon mixtures in the gasoline boiling range suitable for use as motor fuel in internal combustion engines.

One object of the invention is to recover from a stream of light hydrocarbons the maximum quantity which can be made available for use as liquid motor fuel or gasoline. Another object is to combine or intercombine a series of operations or process steps in such manner as to produce directly therefrom or thereby gasoline of desired vapor pressure. Another object is to efiect the above results in a continuous operation on light hydrocarbons having an end point suitable for motorfuels, for example approximately 400 F'., which light hydrocarbons may be separated by fractionation or otherwise from the products of a distillation, catalytic transforming, or thermal cracking zone to which hydrocarbons are charged from any source, either in natural or derived state or blended. Other objects will be apparent from the detailed description which follows.

The initial material to be treated may be derived from any source of hydrocarbons including mineral oil, shale, coal, lignite, etc. and is preferably in the form of a composite hydrocarbon stream comprising or including some hydrocarbons in the desired boiling range. According to the invention, such a stream is subjected to a series of separating andloL m pe tions to segregate therefrom a low vapor pressure gasoline and a cut composed substantially of hydrocarbons of the three and/or four carbon atom group. This cut is subjected to polyand for highest recovery of liquid products, in

eluding dehydrogenation of some or all of the gaseous material issuing from the polymerization zone.

The nature of the invention and the manner of its use is illustrated diagrammatically in the accompanying drawing, the single figure of which shows a complete operative circuit for producing gasoline of desired vapor pressure and'indic'ates a number of alternative modifications.

In the drawing, a composite stream of hydrocarbons of wide boiling range and from any source, including a vaporizing, transforming or cracking zone, as indicated diagrammatically, is conducted by line I to a primary separating zone A containing apparatus of any known or desired type. In the present instance, a fractionating tower or column 2 is indicated, wherein heavier 10 or high boiling hydrocarbons are condensed and from which they are conducted away by line 3, for example, as fuel oil or cycle stock for storage or for immediate consumption or further treatment. An overhead-cut or fraction, preferably comprising allhydrocarbons in the. gasoline boillng range andlighter, is conducted from the top of the tower 2 by line 5| through condenser 4 to separator 5, whence condensate leaves by line 6 which has a branch 1, if desired, for conducting part of the condensate as reflux to the upper 'end of fractionator 2 to control the operating temperatures therein. Gaseous material leaves the upper end of separator 5 by line 8, which conducts the same, with or without additional gaseous material added by branch lines 9 and I I], to an absorption zone B containing apparatus of any suitable or desired type. The absorption system diagrammatically indicated utilizes a circulated liquid medium which enters the top of absorber or stripping tower II and is passed countercurrent to the gaseous charge admitted by line 8, the rich absorbent liquid passing from the bottom of tower ll through heat exchanger I2 and heater l3 into the lower end of vaporizer H, where the absorbed-gasoline vapors are released to leave the top of the absorber by line I 5, the lean absorbent liquid then being pumped back from the bottom of vaporizer l4, through heat exchanger I2 and cooler [6, to be again discharged into the top of stripping tower ll.

a part may be sent back by line l8, if desired,

into the top of vaporizing tower H as reflux.

The gasoline condensate from separator 5, to-

gether with the condensate brought from absorption zone B by line 52, is conducted by line 9 a fitabilizing or debutanizing zone 0 having apparatus of any suitable or desired type to separate out a gasoline having a low vapor pressure. The stabilizing apparatus illustrated comprises a heater l9 and a debutanizing or fractionating tower 29, the low vapor pressure gasoline being withdrawn as a condensed bottoms fraction by line 2|, while the lighter hydrocarbons of the C2, C3 and C4 carbon groups leave tower 20 by overhead line 53, to be conducted through condenser 22 into gas separator 23. Any fixed and incondensible gases are vented from the top of separator 23 into line 9, which joins line 8 leading to absorption zone B. A portion of the condensate from separator 23 may be sent as reflux back into stabilizer 20 by line 24, while the remainder is sent by line 25 to separating zone D, having apparatus of any known or desired type to remove from the condensate the lighter hydrocarbons which are not readily susceptible of polymerization, including those of the C2 carbon group with at least a part of the C3 group. The apparatus indicated comprises a heater 26 and a fractionating tower 27.

- The hydrocarbons to be rejected leave tower 21 by line 28 as an overhead fraction and are withdrawn from the system for such use as may be desired. Reflux to control the operation of the tower will be admitted by line 29 from anysuitable source. The tower is operated so as to produce a selected bottoms or liquid fraction which leaves the tower by line 30 and contains a maximum quantity of unsaturates suitable for polymerization into hydrocarbons in the gasoline boiling range, including the hydrocarbons of the four carbon group. This fraction is utilized both to increase the quantity of gasoline recoverable from the original charging material and the unpolymerized part can be added to the low vapor pressure gasoline in line' 2| to adjust the vapor pressure of the same as may be desired, for example to raise the vapor pressure to that of commercial gasoline. Accordingly, line 30 leads to a polymerizing zone E containing apparatus of any suitable or desired type for producing the desired result. Since the selected fraction is already in liquid phase, it is advantageous to use a low temperature liquid phase operation. One operation of this character which is quite suitable utilizes pressures up to 500 pounds, a temperature range of 50 to 300 and a catalytic mass having suitable selective adsorptive properties, such, for example, as certain blends of silica and alumina of natural or artificial origin. However, any other suitable polymerizing operation, whether liquid phase or vapor phase, may be utilized in zone E.

The products of the polymerizing operation leave the polymerizing zone by line 3|, which conducts them to a cooler or condenser 32. If the liquid polymers formed do not contain substantial amounts of material boiling above the gasoline boiling range, and if the unconverted gaseous material is substantially free of fixed and incondensible gases and hence suitable for absorption by low vapor pressure gasoline to raise the vapor pressure of the same to the desired amount, all liquid and gaseous materials leaving cooler 32 may be sent by line 33 to be added to the low vapor pressure gasoline in line 2| as indicated. If it is desirable to separate the products of polymerization into gaseous and liquid hydrocarbons, the same may be conducted from cooler 32 by line 34 to separator 35. The liquid fraction from the bottom of separator 35 may be conducted by line 38 and thence sent by branch line 31 to be added to the condensate in line 6 passing to separating or stabilizing zone C, or some or all of the condensate may be sent by branch line 38 to be added to the material in primary separating zone A, in this instance to be admitted as reflux into tower 2 at any suitable level, depending upon its boiling range. The gaseous material leaves separator 35 as an overhead fraction by line 39, which conducts it through a cooler or condenser 49, from which some of it (if the cut is rich in unsaturates) may be sent back by line 4| to be added to the selected cut in line 39 for recirculation through the polymerizing zon E. Any desired part or all of the gaseous material may also be sent by line 42 to be added to the low vapor pressure gasoline in line 2| to raise the vapor,

may be sent by line 44 to and through a gas cracking or dehydrogenating zone F containing apparatus of any known or desired type, either thermal or catalytic, which will convert the gases into unsaturates. A dehydrogenating operation I suitable for use in zone F is one effected at low pressure, with a catalyst comprising a blend of chromium oxide and alumina maintained at a temperature in the range of 900 to 1000 F. The products of dehydrogenating zone F are conducted by line 45 through cooler 48 and then by line 41 into branch line H] which joins line 8 leading to absorption zone B, or, alternatively, may be conducted by branch line 48 to join line Si in advance of condenser 4.

If polymerizing zone E produces fixed gases, and it is undesirable to use the circuit which includes dehydrogenation zone F, then suitable gas separating equipment -(not shown) may follow cooler 40, the vent to the separating equipment being suitably joined to branch line ID or branch line 9, so that fixed and incondensible gases and vapors entrained therewith will be conducted to absorption zone B.

Saturated hydrocarbon gases suitable for cracking i'nto unsaturates may be admitted to the system in advance of dehydrogenating zone F, as by valved branchline 49. Light hydrocarbon gases, such as those vented from the separator mentioned in the preceding paragraph, or

which it may be desirable to add to the system from any outside source, may be conducted thereto,. as by line 59 leading into line III in advance oi. absorption zone B.

I claim as my invention:

1. Process of recovering a maximum quantity of commercial gasoline from a composite hydrocarbon stream which comprises subjecting said stream to a series of fractionating operations to segregate therefrom a low vapor pressure gasol ne and a cut composed substantially of hydrocarbons of the four carbon group, subjecting said cut under polymerizing conditions to a polymerizingoperation to convert at least a part of the unsaturates therein into liquid hydrocarbons utilizing the liquid polymers from said polymerizing operation as reflux in one of said fractionating operations so as to augment the quantity of said low vapor, pressure gasoline, and adding to said gasoline suflicient gaseous material from said polymerizing operation to raise the vapor pressure thereof.

2. Process of recovering a maximum quantity of commercial gasoline from a composite hydrocarbon stream which comprises subjecting said stream to a series of fractionating operations to segregate therefrom a low vapor pressure gasoline and a cut composed substantially of hydrocarbons of the four carbon group, subjecting said out under polymerizing conditions to a polymerizing operation to convert at least a part of the unsaturates therein into liquid hydrocarbons, adding the liquid polymers from said polymeriz ing operation to the material charged to one of said fractionating operations so as to augment the quantity of said low vapor pressure gasoline, adding a part of the gaseous materials from said polymerizing operation to said gasoline to raise the vapor pressure thereof and recycling the remainder of said gaseous material directly through said polymerizing operation.

3. Process of recovering a maximum quantity of commercial gasoline from a composite hydrocarbon stream which comprises subjecting said stream to a. series of separating operations to segregate therefrom a low vapor pressure gasoline and a cut composed substantially of hydrocarbons ofthe four carbon group, subjecting said out under polymerizing conditions to a polymerizing operation to convert at least a part of the unsaturates therein into liquid hydrocarbons,

utilizing the liquid polymers from said polymerizing operation as reflux in effecting the segregation of said low vapor pressure gasoline and to augment the quantity of the latter, adding a part of the gaseous material from said polymerizing operation to said gasoline to raise the vapor pressure thereof, and sending the remainder of the gaseous material from said polymerizing operation back into the system in advance of one of said separating operations.

4. Process of recovering a maximum quantity of commercial gasoline from a composite hydrocarbon stream which comprises subjecting said stream to a series of separating operations to segregate therefrom a low vapor pressure gasoline and a cut composed substantially of hydrocarbons of the four carbon group, subjecting said cut under polymerizing conditions to a polymerizing operation to convert at least a part of the unsaturates therein into liquid hydrocarbons, utilizing the liquid polymers from said polymerizing operation as reflux in effecting the segregation of said low vapor pressure gasoline and to augment the quantity of the latter, adding a part of the gaseous material from said polymerizing operation to said gasoline to raise the vapor pressure thereof, subjecting, the remainder of the gaseous material from said polymerizing operation to a dehydrogenating or gas cracking operation toincrease the unsaturates therein and adding the products of the dehydrogenation operation to the hydrocarbon stream fed to one of said separating operations.

5. In the treatment of a composite hydrocarjecting the latter to a polymerizing operation to convert at least a part of the unsaturates contained therein into liquid hydrocarbons, adding liquid polymers from the polymerizing operation tonne of said separating steps to increase the yield of gasoline, using a part of the gaseous material from the polymerizing operation to adjust the vapor pressure of said low vapor pressure gasoline, and recycling the remainder of said gaseous material from the polymerizing operation through the latter.

6. In the treatment of a composite hydrocar bon stream to recover a maximum quantity of liquid hydrocarbons in the gasoline boiling range the process steps which comprise separating from the stream hydrocarbons in the gasoline boiling range and lighter, removing from the last named hydrocarbons the fixed and incondensible gases contained therein, separating the remaining hydrocarbons into low vapor pressure gasoline and lighter hydrocarbons of the two, three and four carbon atom groups, removing from said lighter hydrocarbons those in the four carbon atom group, subjecting the latter to a polymerizing operation to convert at least a part of the unsaturates into liquid hydrocarbons, utilizing liquid polymers from the polymerizing operation to assist in the .first separating step and thereby augment the quantity of low vapor pressure gaso- 

